It has long been known that various solid hydrocarbon-containing mineral materials, such as bitumen-containing mineral materials exemplified by tar sands and oil-bearing diatomites, have great potential as fuel sources. Extensive research has been carried out to develop systems for economical recovery of fuel from such materials. Heretofore, many different systems have been proposed for treatment of such materials, but there have been inadequate incentives for commercial development of these systems because of excessive costs and other drawbacks. In most of the proposed systems, it has been considered important, in the as-mined material, to separate mineral material containing no hydrocarbon from the hydrocarbon containing mineral material to minimize the amount of material being processed; the high cost of effecting the desired degree of such separation has been a major factor in rendering such systems commercially unattractive. Because of such excessive costs, the use of such hydrocarbon-containing materials as sources of oil and gas has not been extensive even though large deposits are known to exist.
Systems have also been proposed employing traveling grates for recovery of oil from oil-bearing shale and other oil-bearing materials. However, these systems have had various disadvantages which have discouraged commercial development.